1. Field of the Invention
The embodiments discussed herein are related to a method of manufacturing a semiconductor device.
2. Description of the Related Art
A conventional trench contact that forms a contact (electrical contact portion) with an electrode in an inner wall of a trench is formed by embedding the electrode inside the trench, which is formed in a semiconductor substrate. As a trench contact, use of a contact between a metal electrode and a part of a semiconductor portion of a gate electrode or source region formed in a surface side of a semiconductor substrate enables increased contact area and low contact resistivity. Further, use of a contact between the semiconductor portion and metal electrode as a trench contact enables reductions in size without increasing contact resistivity.
In a conventional process for manufacturing a semiconductor device having a conventional trench contact, heat treatment by rapid thermal annealing (RTA) may be performed to a titanium (Ti) and titanium nitride (TiN) film formed on walls of the trench. Objectives of performing the RTA treatment are primarily the following two points. The first objective is to convert the titanium film to a silicide, form an ohmic contact with the semiconductor region, and lower contact resistivity. The second objective is to improve the function of the barrier metal by nitriding the titanium atoms (hereinafter, unreacted titanium atoms) that remain unreacted in the titanium nitride film when heat treatment is performed in a nitrogen (N2) atmosphere and the titanium nitride film is formed. Therefore, when the RTA treatment is not sufficiently performed and the nitriding of unreacted titanium atoms does not progress, unreacted titanium atoms remain in the titanium nitride film. In the titanium nitride film, the portion in which unreacted titanium atoms remain reduces the function of the barrier metal and the following problem arises.
When the function of the titanium nitride film decreases as a barrier metal, fluorine (F) atoms included in a source gas (WF6) used in the formation of the tungsten plug enter the titanium nitride film, pass through the titanium nitride film, and reach the lower layer, the titanium film. These fluorine atoms react with the titanium atoms inside the titanium film and at a side surface of the trench, a gap forms between the titanium film and the titanium nitride film whereby the function of the barrier metal further decreases consequent to the titanium nitride film peeling from the titanium film (hereinafter, peeling of the titanium nitride film). To avoid such problems, the RTA treatment is performed at a high temperature of around 700 degrees C. (a range of about 690 degrees C. to 750 degrees C.), the titanium film is converted into a silicide and the unreacted titanium atoms inside the titanium nitride film are nitrided and decrease.
On the other hand, performing the RTA treatment at a high temperature of about 700 degrees C. results in a decrease of the adhesion of the interlayer insulating film and the barrier metal, creating a new problem. The inventor has confirmed that if the adhesion of the interlayer insulating film and the barrier metal decreases, the barrier metal peels and curls away from the interlayer insulating film (hereinafter, peeling of the barrier metal) consequent to ultrasonic vibration, load, etc. applied to wires during wire bonding to join wires to the surface electrode. Barrier metal that has peeled from the interlayer insulating film during wire bonding collects near the joined portion of the wire and the surface electrode, and a portion where no barrier metal is present occurs between the interlayer insulating film and the surface electrode. Such peeling of barrier metal is dependent on the temperature of the RTA treatment and tends to occur more frequently the higher the temperature of the RTA treatment is.
To improve the adhesion of the interlayer insulating film and the barrier metal, a semiconductor device has been proposed in which a titanium-silicon (Ti—Si) film is formed on an interlayer insulating film that is formed in a silicon substrate surface, barrier metal that is formed sequentially by a titanium film and a titanium nitride film is further stacked on the Ti—Si film, and electrode wiring is disposed on the barrier metal (for example, refer to Japanese Patent Application Laid-Open Publication No. H6-314722). In Japanese Patent Application Laid-Open Publication No. H6-314722, formation of the Ti—Si film between the interlayer insulating film and the titanium film prevents the organization near the interface of the interlayer insulating film from becoming vulnerable during the high-temperature heat treatment for reducing contact resistivity of the barrier metal consequent to the metal element titanium configuring the barrier metal.
As a method of forming a contact, a method has been proposed in which a contact hole is formed in an interlayer insulating film, a titanium silicide film is formed by RTA treatment after a titanium film is formed on the interlayer insulating film by chemical vapor deposition (CVD), and thereafter, a titanium nitride film is formed by a plasma CVD method that uses a mixed gas that includes a halogenated titanium compound and nitriding agent (for example, refer to Japanese Patent Application Laid-Open Publication No. H10-112446 (paragraphs 0033 to 0035)). In Japanese Patent Application Laid-Open Publication No. H10-112446, when the titanium nitride film is formed by the plasma CVD method, the titanium film that remains unreacted and contacts the interlayer insulating film reacts with a reactive nitrogen species and is nitrided and thus, converted into a titanium nitride film.
As another method of forming a contact, a method has been proposed in which after a titanium film and a titanium nitride film are sequentially formed along an inner wall of a contact hole on an interlayer insulating film, an exposed portion of the titanium film is nitrided by RTA treatment at 650 degrees C. in a nitrogen atmosphere to form a titanium nitride film (for example, refer to Japanese Patent Application Laid-Open Publication No. H11-145085 (paragraphs 0007, 0009, and 0015)). In Japanese Patent Application Laid-Open Publication No. H11-145085, before the formation of a tungsten plug, an exposed portion of a titanium film is converted into a titanium nitride film, whereby peeling of the tungsten plug formed thereafter can be prevented. Further, in Japanese Patent Application Laid-Open Publication No. H11-145085, a method nitriding the exposed portion of the titanium film by a plasma nitriding process is further proposed.
As yet another method of forming a contact, a method has been proposed in which before a tungsten plug that is connected to a titanium nitride film exposed in a contact hole is embedded in the contact hole, a plasma nitriding process is performed with respect to an inner wall of the contact hole (for example, refer to International Publication No. 2007/110988 (paragraphs 0039 to 0045)). In International Publication No. 2007/110988, before the tungsten plug is embedded in the contact hole, the plasma nitriding process is performed at a substrate temperature of 350 degrees C. and an inner wall of the contact hole is nitrided, whereby moisture-barrier property of the inner wall of the contact hole is enhanced.
Nonetheless, in Japanese Patent Application Laid-Open Publication No. H6-314722, although adhesion of the interlayer insulating film and the barrier metal can be enhanced by the Ti—Si film, formation processes for the Ti—Si film and an etching process for patterning the Ti—Si film have to be added and as result, manufacturing processes become complicated. Further, in Japanese Patent Application Laid-Open Publication No. H10-112446, since RTA treatment is performed between the formation of the titanium film and the formation of the titanium nitride film without continuous formation of the titanium film and the titanium nitride film that become the barrier metal, processes are difficult. In Japanese Patent Application Laid-Open Publication No. H11-145085 and International Publication No. 2007/110988, contact resistivity may increase as a result of a silicide not forming between the titanium film and silicon since the heat treatment temperature is low.